Sixty Northwest species, including the Oregon spotted frog, the Seattle area's Lake Sammamish kokanee and 32 types of slugs and snails, will be considered for federal endangered species protection under an agreement filed with a judge this week.

The agreement between the environmental group Center for Biological Diversity and the U.S. Fish & Wildlife Service dictates that the service must decide by 2018 whether to add plants and animals to the endangered species list. The agreement, pending with a federal judge in Washington, D.C., applies to 757 species across the country and five dozen in the Northwest.

Of the 757 species, the 258 already on a "candidate" list for protection have the best chance of being classified as endangered or threatened under federal law, said Noah Greenwald, the center's endangered species program director in Portland.

The wildlife service will make decisions on the species in a series of steps over the coming years. First up are decisions on the 32 mollusks, the kokanee -- a freshwater salmon -- and the dusky tree vole, which favors old-growth forest habitat in northwestern Oregon. The agency will decide this year whether to propose them for protection or determine they don't qualify.

In a news release, the wildlife service said the agreement will allow the agency to focus its resources on the species that most need protection. It also provides clarity and certainty regarding when listing decisions will be made, the agency said.

A decision on the spotted frog is due in 2013. It's been a candidate for listing since 1991, and the Center for Biological Diversity petitioned to list it as endangered in 2004. The frog stands a decent chance of gaining protection, Greenwald said.

The Pacific fisher, a cat-like animal related to minks and otters, also has been a candidate for listing since 2004 and appears likely to gain protection, he said.

The most famous animal on the endangered species list is the northern spotted owl, which was listed as threatened in 1990 and has been at the center of lawsuits, research and logging shutdowns ever since.

Greenwald agreed that species-by-species decisions are difficult and broader habitat preservation may make more sense.

"Both approaches are necessary, I think," he said. "The individual species does matter. Often they represent the best of what's left of the habitat or ecosystem."

The fisher needs old-growth forest habitat, he said, while the spotted frog prefers the flood plain and is an excellent indicator species of wetlands health.